The present invention generally relates to refrigeration devices. More particularly, the present invention relates to defrost cycle controllers for refrigerators and freezers.
As is known, refrigerator and freezer systems, especially of the home appliance type, provide cooled air to an enclosure in which food and the like can be stored, thereby to prolong the edible life of the food. The enclosures, namely refrigerators and freezers, are cooled by air blown over heat exchangers, the heat exchangers extracting heat from the air thereby producing cooled air. The heat exchangers generally operate on the known cooling effect provided by gas that is expanded in a closed circuit, i.e., the refrigeration cycle. However, to be expanded, the gas must also be compressed and this is accomplished by the use of a compressor.
The efficiency of the systems can be enhanced by reducing the amount of frost that builds up on the heat exchanger, as is known. Modern systems are generally of the self-defrosting type. To this end, they employ a heater specially positioned and controlled to slightly heat the enclosure to cause melting of frost build-up on the heat exchanger. These defrost heaters are controlled pursuant to defrost cycle algorithms and configurations.
As a result, these freezers-refrigerators undergo two general cycles or modes, a cooling cycle or mode and a defrost cycle or mode. During the cooling cycle, a compressor is connected to a line voltage and the compressor is cycled on and off by means of a thermostat, i.e., the compressor is actually run only when the enclosure becomes sufficiently warm. During the defrost cycle, the compressor is disconnected from the line voltage and instead, a defrost heater is connected to the line voltage. The defrost heater is turned off by means of a temperature sensitive switch, after the frost has been melted away.
Generally, there are three known ways or techniques for controlling the operation of such a compressor and such a defrost heater with what is referred to herein as a defrost cycle controller. These three ways are referred to herein as real or straight time, cumulative time, and variable time.
The real time technique involves monitoring the connection of the system to line voltage. The interval between defrosts is then based on a fixed interval of real time.
The cumulative time method involves monitoring of the cumulative time a compressor is run during a cooling interval. The interval between defrost cycles is then varied based on the cumulative time the compressor is run.
The variable time method is the most recently adopted method and involves allowing for variable intervals between defrost cycles by monitoring both cumulative compressor run time as well as continuous compressor run time, and defrost length. The interval between defrost cycles then is based more closely on the need for defrosting.
As is known, during a defrost cycle there is also dripping of melted frost to a drip pan from which the melted frost evaporates. This is known as the drip mode or cycle and those terms are used herein.
Among others, the United States government has continuously enacted more and more stringent laws and regulations relating to the efficiency of refrigerators and freezers, particularly as home appliances. As a result, much research has been directed to more effective control over the refrigeration cycles of refrigerators and freezers and, particularly, to the defrost cycle, since in this cycle, the effect of refrigeration is, on the one hand, counteracted by removing cold from the enclosure, and on the other hand, enhanced by increasing the efficiency of refrigeration by removing insulating frost.
Patents directed to defrost controllers include:
______________________________________ U.S. Pat. No. 4,156,350 Refrigeration Apparatus Demand Defrost Control System and Method U.S. Pat. No. 4,411,139 Defrost Control System and Display Panel U.S. Pat. No. 4,850,204 Adaptive Defrost System with Ambient Condition Change Detector U.S. Pat. No. 4,884,414 Adaptive Defrost System U.S. Pat. No. 4,251,988 Defrosting System Using Actual Defrosting Time as a Controlling Parameter ______________________________________
The teachings of these patents are incorporated herein by reference.